This invention relates to radar apparatus of the type which transmits groups of pulses, each group including a long pulse for detecting or tracking long range targets and a short pulse for detecting or tracking short range targets.
One such radar apparatus is described in U.K. Patent Specification No. 1552877 and discloses groups of pulses each consisting of a single long pulse, which is frequency swept, followed by a single short pulse, which has a frequency outside a frequency range of the long swept pulse. Additional short pulses are inserted between the groups to increase the pulse repetition frequency of the short pulses.
In radar apparatus of the aforementioned type, it is necessary for initial stages of the receiver to process both the long pulses and the short pulses though these may be separated out into different channels in latter parts of the receiver. A problem arises in the detection of a short range target close to another larger target or to a source of clutter. This larger target (or source of clutter) will produce a strong return signal which will saturate the initial stages of the receiver; i.e. cause "limiting." Should the return of the short pulse from the smaller target be received whilst the receiver is thus saturated, the receiver will fail to detect the short pulse and the small target will not be indicated on the radar output.